What is the best way to add terms and conditions to a jotform? Our T&C's are long.

If you have a long Terms and Conditions, I would recommend using the Short Scrollable Terms widget. This widget allows you to insert the Terms and Condition in a scrollable section so you can save up some space on your form, it also has the checkbox to ensure that your user has read the terms.

Here's the link to the widget: https://widgets.jotform.com/widget/short_scrollable_terms 
To use a widget for your form, please follow this guide: How to Add a Widget to your Form.

You can check out our demo here: http://form.jotformpro.com/form/51163381270953

We also have another Terms & Conditions widget that you can try if you have a website that contains the Terms and Conditions. You can use this widget to make a clickable link to that webpage. https://widgets.jotform.com/widget/terms__conditions 

If you need further assistance, please let us know.
Regards.